The partial replacement of cement with industrial wastes, especially in the concretes with high volume of cement-based materials such as ultra-high performance concretes (UHPC) may have positive effects on the environment and could lead to improvements in concrete properties. However, the effects of some types of these materials, such as coal waste and copper slag, have not been investigated seriously. In this study, the effects of several cement-based materials with different pozzolanic reactivity from very active (like silica fume) to approximately inactive (like silica powder) have been studied on the UHPC properties. Since the treatment temperature of 70-100 0C intensifies the possibility of delayed ettringite formation, thermal curing at 60 0C and 90 0C have been selected as the treatment temperatures of low and high risk of delayed ettringite formation, furthermore the results have been compared with the standard thermal curing at 20 0C. An electrical conductivity method has been used to compare the pozzolanic reaction rate of materials. In this study, compressive strengths, modulus of rupture and rapid chloride migration coefficients have been determined and the investigation of microstructure has been carried out using scanning electron microscopy. The obtained results show that use of heat treatment for the mixtures incorporating materials with low pozzolanic reactivity may reduce the strength and durability of ultra-high performance mixtures. The differences between the results obtained from the thermal curing conditions of 60 0C and 90 0C were not significant, however use of thermal curing at 90 0C requires higher energy demand compared with the thermal curing at 60 0C, moreover higher risk of delayed ettringite formation is expected.

[1] P.R. Rangaraju, J. Olek, S. Diamond, An investigation into the influence of inter-aggregate spacing and the extent of the ITZ on properties of Portland cement concretes, Cement and Concrete Research, 40(11) (2010) 1601-1608.